An analog to digital converter (ADC) is a commonly used circuit, mainly adapted to convert analog signals into digital signals. When a server is designed, ADC circuits are often used for monitoring voltage of each channel within the server or to identify ID voltages of different boards. In the field of conventional ADC circuits, it is common to use ADC chips with an inter-integrated circuit (I2C) type or to use differential ports of a CPLD so as to design an ADC-based conversion circuit using RC integration principle.
However, it would cost a lot if ADC chips with I2C type are used. If differential ports of a CPLD are used, then the conversion circuit, designed according to the integral comparators of the ADC, is limited by the feature of nonlinearity of the RC circuit as well as errors related to CPLD port potential comparators. As a result, the practical accuracy of the conversion circuit is significantly reduced.